Demodulator device for frequency and amplitude modulation



E. H. LANGE'. DEMODULATOR DEVICE FOR FREQUENCY July 20, 1948.

AND AMPLITUDE MODULATIONS Filed Nov. 5, 1945 INVENTO R Patented July 20,1948 UNITED STATES PATENT OFFICE DEMODULATOR DEVICE FOR FREQUENCY ANDAMPLITUDE MODULATION i 21 Claims.

This invention relates to demodulators for carrier waves havingfrequency-modulation or amplitude-modulation, or having both of thesemodulations, and more particularly to such demodulators in connectionwith receiving systems for these carrier waves.

The principal object of this invention is to provide such demodulatordevices with economy and simplicity of component circuit parts andelectronic equipment, and with improved facilities for tuning, forcompensating amplitude-modulation, and for control of average signalamplitudes.

A first object of this invention is to provide unilaterally-groundedoutput voltages forthe series-parallel circuit typefrequency-demodulator described in U. S. Patent 2,369,055, of February6, 1945, and more particularly to provide such operation with directanode-cathode series connection of the series-parallel circuit asdistinguished from a shunt supply of said circuit, and with adouble-diode rectifier employing diodeanodes each capable of thermionicconductance with said cathode, and in the same tube with the commoncathode.

A second object of this invention is to provide suchunilaterallygrounded output voltages upon a conductive connection toground, and to provide sustained output voltages which persist as longas a frequency deviation exists between the carrier wave and the centreor balance-frequency of the demodulator, for use in controlling thefrequency of waves impressed upon the demodulator, for example in asuperheterodyne receiver, and

when receiving either amplitude-modulation or frequency-modulation.

A third object is to prow'de simple separating means for separating or'annulling the voltages of carrier frequency from the desired outputvoltages of modulation frequency.

A fourth object is to provide filter means for demodulators of theunilaterally-grounded common cathode type, whereby the grid. controlmeans of a pre-amplifier coupled with such a demodulator is suppliedwith either amplitudeenvelope responsive and opposing voltages forreducing undesired amplitude-modulation, or average-amplitude responsivevoltages for regulating signal strength employed, or both, and through aconductive path between the ground and said grid control means of thepre-amplifier.

A fifth object of this invention is to provide the features stated inthe second to fourth objects inclusive through simple structures,applicable also to other types of demodulator circuit than I designatedin the first object, and. also employing a common cathode typedouble-diode rectifier for supplying such unilaterally-grounded outputvoltages. r

A sixth object is to provide resistance-capaci tance filter means in thecommon cathode type demodulators of this invention, for transferring tothe quadrature-phase controlling grid of an oscillator orreactance-modulator connected with an oscillator in a superheterodynereceiver, sustained voltages, determined by the amount and algebraicsign of the difference between the balance-frequency of the demodulatorand the centre-frequency or unmodulated frequency of the carrier wave,independent of the presence of frequency-modulation upon the carrierwave, and for alignment of tuning in the receiver.

A seventh object of this invention is to provide simpleimpedance-balance means for annullin or substantially reducing. minorimpedanceasymmetry introduced by unilateral impedance connections ofthis invention.

ture-phase or frequency-controlling grid, of a thermionic generatorsystem, and with means employable for compensating impedance-asymmetry.Fig. 2 illustrates a pre-amplifier coupled with the input-impedance ofone'of the demodulators of this invention, and a transfer-filter meansfor transferring control voltages from a common conductive path-betweenthe diode-anodes and the cathode of the demodulators of this invention,and illustrated with particular reference to the demodulator of Fig. 1.;v v

Fig. 3 illustrates application of the principles and structure of thisinvention toanother type of demodulator circuit.

Referring to the figures, at His athermionic tube having the cathode l4,cathode-terminal Ida, the diode-anodes l2 and I3 each capable ofthermionic conductance with the common cathode I4; also having acontrol-grid l9 connected through input-impedance 20 and conductor 2| toterminal Illa, which terminal is either directly connected to terminalMa, or connected to terminal 14a through a bias-resistance I having oneterminal connected to terminal Ma. At i6 is a third anode capable ofthermionic conductance with the common cathode [4, it being understoodthat thermionic conductance between the third anode l6 and cathode I4 iscontrollable by the control-grid [9 between cathode l4 and anode l6.' Atll, Fig. 1, is shown a suppressorgrid directly connected to cathodeterminal Ma and at I8 is a screen-grid understood to be connected to apositive terminal upon the source 24 of unidirectional voltage, thesource 24 having its negative terminal connected to ground 22. Forsimplicity of illustration the suppressor-grid l1 and screen-grid l8 areomitted from Figs. 2 and 3, tube l5, however it will be understood thatthese grids may be present and similarly connected in these figures, forcontrolling the transconductance and impedance properties in amannerwell understood;

One of'the diode-anodes, for example diodeanode I2 is connected directlyto ground 22 through conductor 22- oi negligible impedance. At 111 is ajunction-terminal upon a phase-shifting networkiconnected to thediode-anodes i2 and i3 and to the common cathode I l, and betweenjunction-terminal m and common cathode I4 is acorn-men conductive pathfor thermionic currents of both diode-anodes l2 and I3.

ReferringtoFig, 1, the positive terminal of source' 24 is directlyconnectedthrough conductor 25 to the third anode it of tube l5. Forpurposescf illustration it will be understood that the source ofunidirectional voltage 24 may be a battery or'other we'l'l know-n means,and having a conductive path from thepositive terminal to ground such asillustrated by resistance 5, for unidirectional components of current.At 9 is an inductance coil, and at 8 is a variable condenser connectedacross the terminals of coil 9, and for tuning coil 9 to resonance withthe carrier frequency impressed upon input-impedance #20. At 6 is ahigh-frequency choke-coil connected between the cathode-terminal Ila-and the junctionterm-ina-l m upon the inductance coil 9, thejunction-"terminaim being between the terminals b and d of theinductance coil 9, which terminals are connected to condenser 8."similarly connected in Fig. 2, except that series resistance may beincluded in the conductive path from junction-terminal m tocathode-terminal 'M a 'as hereafter pointed out. I

Terminal d is connected through vdiode-resistor 1' to terminal p ofdioderesistor T, which terminal p is directly connected :to diode-anodei3; likewise terminal b is connected through diode-resistor -r' toterminal -q of diode-resistor 'v" ,which terminal g isdirectlyconnectedtodiodeanode l2. Diode-resistor -r is shunted iby. oondenser45, andlikewise diode-resistor -1" isshunted condenser '46.Terminals d and b are similarly connected in Fig.2. At K-is aswitch-blade understood to'be-directly connected by connector are to thecontrol-grid of anamplifier for amplifying-thedemodulated voltagesoieither amplitudemodulation or frequency-modulation, and theswitch-terminal indicated by :A. for amplitude modulation is directlyconnected to the tor-- minal of diode-resistor =1" opposite the terminal"q 'of 'said resistor, that is to terminal b. The switch terininalindicated by F. M; forirequencymodulation-is connected through coil'l'by way of conductor 1 to the "terminal pof diode-resistor Choke-coil isI r. Coil l is understood to be inductively coupled with coil 9, and tobe so connected in the circuit through conductor I that the resultantalternating voltage of carrier frequency in the circuitq-rb-9drp--I-l-F. M. is substantially zero, the magnitude of voltageinduced in coil 1 by carrier frequency of coil 9 being understood to beequalized with the magnitude of alternating voltage in coil 9. Connectedin series between the terminal and ground 22 is the filter-resistance 28connected to the terminal F. M. and the filter-condenser 29 connected toground 22. The junction between filter-resistance 28 andfilter-condenser 29 is understood to be connected by the conductor Gqoto the frequency-controlling grid of a thermionic generator system of asuperheterodyne receiver, for example to the quadrature-p-hasecontrolling grid of a thermionic oscillator, or reactance modulatorconnected with a generator, and for modifying the resultant carrierfrequency impressed upon the inputr-impedance 20.

At 2v is a high-frequency choke-coil having. one terminal connected tothe ground 22, and the other terminal 3 connected to the junctionetereminal m. At 2' is another high-frequency chokecoil having one terminalconnected through condenser u to the ungrounded diode-anode, for examplediode-anode l3, and the other terminal connected to the switch-blade K"which is con.- nectable to switch-termina1-3 I connected to the 1331:-minal s of the chokeecoil 2. Choke-coil 2 is simie larly connected inFig. 3; likewise it will be under: stood that the choke-coil 2- forcompensating impedan'ceeasymmetry is similarly connectable in Fig. 3between the terminal s of choke-coil 2 and the ungrounded diode-anode13.

Referring to Fig. 3., third anode i6 is connected through the primarycoils 9'?) and 91av in series to the positive terminal of source 24, andbyapass condenser 23 is connected from ground conducr tor22 to thepositive terminal of source 29 as in Fig. 1. Coil 9191s inductivelycoupled with coil 9'71, and coil 9a is'inductively coupled with coil 9m,and coils 9a and 9b are connected in series. at the junction-terminal m,the terminal 11 of coil 9b opposite terminal m being connected throughdiode-resistor r to diodeeanode. l3, and the. terminal b of coil 9aopposite terminal m being connected through diode-resistor r todiode-anode l2. Terminal m is connected to cathodeeter-minal I l-athrough the bias-resistance Hi. It will be understood thatbias-resistance i0 is for introducing a small voltage drop through flowthere.- throughof steady. component of current from third anode I6 tocathode 1A, for negatively bias.- ing the control-grid Hi. from cathode14; that the employment of such negative biasing means optional.Negative bias voltage so introduced biases the diode-anodes. from, the,cathode it, however when small amounts .of such bias are employed inrelation to the maximumvol-fia esfimployed upon the diode-anodes fromthe network, such small amounts do not appreciably af ect the operationof the demodulator. It will be under.- stood that the condenser Hshunted across the bias-resistance. 10 has a small impedance in re;lation to resistance H1 for the low or modulation frequencies, and thatsuch biasing means may also be employed inFig. -1, similarly connectedto cathode IA and in series with coil 5, between terminal lfla andterminal l,.4,a. ,Gpil 9b is shunted :by tuning condenser 8b, andlikewise coil 9a -is shunted 'by tuning condenser dd; these tuningcondensers may :be mechanically connected as indicated by connection 50,indicating anelectricallyinsulated mechanical connection between rotorsof condensers 8a, 8b. Tunablecircuits between terminals mb' and betweenm-d' are understood to be spaced as-to tuning, the carrier frequencybeing intermediate with reference to resonance frequencies set bycondensers 8a-and 8b, as hereafter further pointed out. At la is aninductance coil inductively coupled with coil 9a, and at lb is anotherinductance. coil inductively coupled with coil 91). Coils la and lb areconnected in series, one terminal of coil 1b being connected to theungrounded diode-anode I3 and one terminal of coil Ia being connected tothe terminal F. M. of the selector switch having switch-blade K, asheretofore described. It will be understood that coils 1a. and lb areeach so connected in the series circuit 22r'--b-m d 1 |b--'|a--F. M.that thecarrier-frequency voltage in 9b is equalized by thecarrier-frequency voltage in 1b, and likewise the voltage in 9aequalized by the voltage in la, leaving only the resultant of therectified voltages across 1" and r in said series circuit, theresultantvoltage of carrier-frequency being substantially annulled.

Referring to Fig. 2, at 32 is a thermionic tube of a pre-amplifierhaving an output-impedance 20a coupled with the input-impedance 20, forexample of demodulator of Fig. 1, and for transferring voltages ofcarrier frequency to inputimpedance 2| Tube 32 is understood to have acathode 35 connected to ground 22, for example through a bias-resistor,to have a control grid 33 connected to one terminal of the input coil20b of the mare-amplifier, and tohave an anode 34 connected with thepositive terminal of a source of unidirectional voltage throughoutput-impedance 20a, or otherwise energized from a unidirectionalvoltage source. Control-grid 33 is understood to control thermioniccurrents between anode 34 and cathode 35; also it will be understoodthat other grid controls may be present such as a screen-grid andsuppressor-grid between the anode 34 and control-grid 33, forcontrolling currents between anode 34 and cathode 35, and'forcontrolling transconductance and impedance characteristics of tube 32,in a manner well known, and with particular reference totransconductance of control-grid 33. Connected in series in theconductive path between junctionterminal m and the terminal |4a ofcathode I4, is the control-resistor r, connected between thejunction-terminal "m and the terminal .9 of the high-frequencychoke-coil 2 one terminal of control-resistor r being directly connectedto junction-terminal m. Control-resistance 1'" is shunted by thecontrol-condenser 31. Connected between the junction-terminal m and theground 22, is the high-frequency choke-coil 2a in series with thehigh-frequency by-pass condenser 38, one terminal of coil 2a beingconnected to junction-terminal m and one terminal of condenser 38 beingconnected to ground 22. Shunted across the terminals of by-passcondenser 38 is the fllter resistance 39 in series with thefilter-condenser 40, one terminal of resistance 39 being connected toground 22 and one terminal of condenser 40 being connected to theungrounded terminal of condenser 38. The common terminal 43 betweencondenser 40 and resistance 33 is connectable by switch-blade K throughconductor 45 to the terminal of the input coil 23b of the pre-amplifier,opposite the'terminal of said coil connected to control-grid 33'of tube32. Likewise shunted across the terminals of by-lpass condenser 38 isthe filter-resistance 42 in series with the filter-condenser 4|, oneterminal of condenser 4| being connected to ground 22, and one terminalof. resistance 42 being connected to the ungrounded terminal ofcondenser 38. r The common terminal 44 between resistance 42 andcondenser M is connectable by switch-blade K through conductor 45tocontrol-grid 33 of tubev 32, through input coil 20b.

7 It will be understood that the control-resistor r" shuntedby condenser31 illustrated with reference to Fig. 1 can be likewise connected in thestructure of Fig. 3, in the common conductive path between cathode l4and junction-terminal m, and between the junction-terminal m and theterminal 8 of choke-coil 2.

Condensers 45, 46, and 31, shuntedrespectively across the resistances r,r, and 1", are understood to be for smoothing out the unidirectionalvoltages set up across these resistances by unidirectional currentsrespectively to diode-anode l3, diode-anode l2, and to both of thesediodeanodes, and to provide a time-constant sufiiciently large inrelation to the half-cycle time of the carrier wave to smooth out therectified pulses of carrier frequency.

Referring to Fig. 1, operation of the devices will be evident from thefollowing further considerations. The path for the unidirectionalcurrent component fromiground 22 through source 24, and third anode IEto cathode I4, is completed through choke-coils 6 and 2 in series toground 22. When high-frequency voltage is impressed upon theinput-impedance 20 currents of corresponding-carrier frequency are setup in the external network between cathode-terminal Ma and ground 22.The effective impedance ofthe external network is that of theseries-parallel circuit composed of the choke-coil 6 in series with theparallel resonant circuit between the terminals mb; substantially equalvoltages of carrier frequency are present upon the parts m--b and d-m ofinductance coil 9, the parallel circuit between terminals m-b operatingas a pure resistance when tuned to the carrier frequency.

The high-frequency voltages impressed between cathode and diode-anodes|2, |3, are thus com posed of a vector sum of voltages for onediodeanode and a vector difference for the other diodeanode, as detailedin the U. S. patent previously referred to; in the series circuit fromground 22 to conductor the resultant rectified voltage can thus be madezero for a specific carrier frequency, positive for frequency deviationstherefrom of the carrier frequency, and negative for frequencydeviations of opposite algebraic sign.

The choke-coil 2 is many times larger in inductance value than theinductance of the part m-b of coil 9; choke-coil 2 is neverthelesssubstantially in shunt with terminals m-b, the reactance of condenser 46for carrier frequency being substantially smaller than the reactance ofcoil 2, and the equivalent inductance across the terminals m-b is thusslightly smaller than the inductance of the part mb of coil 9. Thejunction-terminal m is normally the mid-inductance point upon the coil9, however it will be understood that this position may beadvantageously slightlymodified when no impedance-compensation isemployed for compensating impedanceasymmetry of the network, introducedfor example bycoil 2. The reactance of coil 2 is also substantiallyhigher than the equivalent resistance at resonance of the parallelresonant circuit m-b and m-d-b, and the total alternating current asdistinguished from a shunt-supply of alternating currents to aphase-shifting network, combinations of shunt and series supply, orother network couplings; said structure providing unilaterally-groundedoutput voltages, and providing sustained voltages to ground for afrequency-controlling grid of a thermionic generator ill]. asuperheterodyne receiver, whenever a sustained difference occurs betweenbalance-frequency of the demodulator and centre-frequency of the carrierwave. When the filter means of Fi 2 is employed with Fig. 1, the simpleonetube demodulator structure provides dynamic stabilization ofamplitude-envelope and regulation of average carrier amplitude employed,with the pro-amplifier. It will be evident that the demodulator of Fig.1 provides economies of circuit elements with reference to Fig. 3.

While I have described and indicated several systems for carrying out myinvention, it will be apparent to one skilled in the art that theinvention disclosed herein is not limited to theparticular organizationsshown and described, but that many modifications may be made withoutdeparting from the scope of my invention.

What is claimed is:

1. A frequency-discriminator for providing unilaterally-grounded outputvoltages responsive in magnitude and polarity to modulation of frequencyof a high-frequency carrier wave, having a thermionic tube with acathode, a first and a second diode-anode with said cathode, a thirdanode, and grid control means for controlling thermionic currentsbetween said third anode and cathode, an input-impedance connectedbetween said grid control means and said cathode, a unidirectionalvoltage source with positive terminal connected to said third anode andnegative terminal connected to ground, a phase-shifting networkconnected between said cathode and i said diode-anodes including acommon conductive connection between said cathode and each of saiddiode-anodes, and a junction-terminal of said conductive connection uponsaid network} a conductive ground connection of negligible impedance toone of said diode-anodes, a high-frequency choke-coil connected betweensaid ground and said junction-terminal, and a high-frequency voltageneutralizing device including a conductive neutralizing-impedancecoupled with said network for transferring opposing high-frequencyvoltages therefrom, and a conductive connection through saidneutralizing-impedance to the ungrounded diode-anode.

2. In combination with the structure of claim 1, a pre-amplifier havinga thermionic tube with grid control means and an output circuitcoupledwith said input-impedance, an amplitude-modulation responsivecontrol-impedance connected in series ,with said common conductiveconnection, having one terminal thereof connected to saidjunction-terminal and the other terminal thereof connected totheungrounded terminal of said choke-coil, and a transfer-filterconnected to said control-impedance including a resistance-capacitanceseries connection with one terminal of the resistance thereof connectedto said ground, and another terminal of said resistance thereofconnected to said grid control means of said preamplifier, fortransferring amplitude-modulation opposing pulses to said pre-amplifiergrid control means to reduce undesired amplitude-modulation, when therate of change of said carrier anllplitudes exceeds a predeterminedminimum va ue.

1 ii 3. In combination with the structure of claim 1, a pre-amplifierhaving a thermionic tube with grid control means and anoutput circuitcoupled with said input-impedance, an amplitude-modulation responsivecontrol-impedance connected in series with said common conductiveconnection, having one terminal thereof connected to the ungroundedterminal of said choke c'oil and the other terminal thereof connectedto'said junction-terminal, and a transfer-filter connected to saidcontrol-impedance including a second highfrequency choke-coil connectedin series with a high-frequency by-pass condenser between saidjunction-terminal and said ground, one terminal of said secondchoke-coil being connected tosaid junction-terminal, and one terminalof-said bypass condenser being connected to said ground, and impedancemeans shunted across said bypass condenser connected with the gridcontrol means of said pre-amplifier.

4. A frequency discriminator for providing unilaterally-groundedsustained output voltages responsive in magnitude and polarity todeviation of frequency of a high-frequency carrierwave, having athermionic tube with a cathode, a first and a second diode-anode withsaid cathode, a third anode, andgrid control means between said cathodeand third anode, resonance-circuit means responsive to saidhigh-frequency carrier wave,

ground, and a high-frequency choke-coil connected between said groundand said cathodeconnected junction-terminal upon said resotrance-circuitmeans common to said conductive circuit connections. a

5. In combination with the structure of claim 4, aneutralizing-impedance for neutralizing high-frequency voltagessuperposed upon ,said output voltages, a conductive connection totheungr-ounded diode anode serially including said neutralizing-impedance,and, a coupling means for coupling said neutralizing-impedance with saidresonance-circuit means.

6. A demodulator for demodulating frequency.- modulation from ahigh-frequency carrier wave, having a thermionic tube with a cathode, afirst and a second diode-anodewith said cathode, a third anode, and gridcontrol means for controllingthermionic currents between said thirdanode and cathode, a three-branch impedance network having a commonjun-ction,,and having a first conductive impedance branch including afirst inductance coil connected between said. junction and one of saiddiode-anodes, a second conductive impedance branch including a secondinductance coil connected between said, junction and the other of saiddiode-ano-des, and a third conductive impedance branch connected betweensaid junction and said cathode; energizing means for said networkincluding a source of unidirectional voltage with positive terminalconnected to, said third anode and negative terminal connected toground, a conductive connection of negligible impedance from one of saiddiode-anodes to said ground, a high-frequency choke-coil connected fromsaid ground to said common junction, and

ahigherreduency voltage balancin means for balancing-out: thehighs-frequency voltage in an output circuitfor demodulated voltages,including a; conductive connection from the ungrou-nded dibdc-anodethrough abucking-coil inductively coupled with said first and secondinductance coils '7, A frequency-demodulator for providingunilaterally-grounded sustained output voltages responsive in magnitudeand polarity todeviation of frequency of a high frequency carrier wave,having a thermionic tube with a cathode, a first and a seconddiode-anode with said. cathdc, ,a third anode, and a control grid forcontrolling currents between said third anode and cathode, a source ofunidirectional voltage with positive terminal connected to said thirdanode and negative terminal connected to ground, a series-parallelcircuit including an inductance coil with terminals shunted by acondenser tuned to said carrier frequency, with a first choke-coilhaving one terminal. connected to said cathode and the other terminalconnected to the mid-- inductance point upon said inductance coil, adiode-resistor shunted by capacitance connected between one of saiddiode-anodes and a terminal :oi said inductance coil, a seconddiode-resistor shuntedlbya second capacitance con-nected between theother diodeeanode: and the other terminal of. said inductance coil, aconductive connection of negligible impedance from one of saiddlode-anodes-to said ground, a second choke- 7, selector means forselecting demodulated voltages, including a switch-terminal connected tothe ungrounded terminal of the diode-resistor having a groundedterminal, and a switch-terminal connected to the other terminal of saidsecond inductance coil, respectively for reception ofamplitude-demodulated voltages or for frequency-demodulated voltages.

9. In combination with the structure of claim 7,, the circuit connectionto said ground from the other terminal of said second inductance coilserially including a filter-resistance and a filtercondenser, saidfilter-condenser having a terminal thereof connected to said ground, fortransferring the sustained voltages across said filtercondenser fromsaiddemodulator, independent of frequency-modulation upon said carrier wave,and dependent as to magnitude and polarity upon the deviation of thecentre-frequency of said carrier wave from the tuned frequency of saidinductance coll shunted by said condenser.

10. In combination with the structure of claim 6, a secondhigh-frequency choke-coil connected in series with a condenser from saidungrounded diode-anode to said common junction, for compensatingimpedance-asymmetry introduced by the first said choke-coil.

11, In combination with the structure of claim 1, a secondhigh-frequency choke-coil connected in series with a condenser from saidungrounded diode-anode to said junction-terminal, for com pensatingimpedance-asymmetry introduced by the first said choke-coil.

12. In a frequency-discriminator for providin sustainedunilaterally-grounded output voltages responsive in magnitude andpolarity to frequency deviations of a high-frequency carrier Wave,having a thermionic tube with a cathode, a first and a seconddiode-anode with said cathode, a third anode, and a control grid forcontrolling currents from said third anode, a carrier frequencyresponsive network having a common conductive connection to said cathodefrom a junction-terminal thereon conductively connected to each of saiddiode-anodes, a conductive connection of negligible impedance to groundfrom one of said diodeanodes, and a high-frequency choke-coil connectedbetween said ground and said junction-terminal, the filter dcvice fortransferring voltages of modulation frequency from said network,including a control-resistance shunted by a contro1-capacitance andconnected in series with said common conductive connection between saidjunctionterrninal and the ungrounded terminal of said choke-coil, asecond high-frequency choke-coil connected to said junction-terminal andin series with a high-frequency by-pass condenser connected to saidground, and circuit connections from the terminals of said by-passcondenser for transferring amplitude-modulation responsive voltages.

13. In combination with the structure of claim 12, a pro-amplifier forsaid frequency-discriminator, having a thermionic tube with grid controlmeans and an anode coupled with said control grid of said discriminator,a filter-resistance connected to said ground and in series through afilter-condenser to the ungrounded terminal of said by-pass condenser,and a connection from said grid control means of said pro-amplifier tosaid ground including a circuit through said filter-resistance. v I

14. In combination with the structure of claim 12, a pre-amplifier forsaid =frequency discriminator having a thermionic tube with grid controlmeans and an anode coupled with said control grid of said discriminator,a filter-condenser con nected to said ground and in series through afilter-resistance to the ungrounded terminal of said by-pass condenser,and a connection from said grid control means of said pro-amplifier tosaid ground including a circuit through said. filter-resistance.

15. In a frequency discriminator having a thermionic tube with cathode,anode, grid control means between said cathode and anode for controllinganode-cathode currents, and a first and second diode-anode with saidcathode, a bilateral phase controlling network with a conductiveconnection to said cathode, a unidirectional voltage source withpositive terminal connected to said anode, a first voltage-rectifyingmeans including a conductive circuit from one of said diode-anodes tosaid cathode through said network and through a first diode-resistor,and a second voltage-rectifying means including a conductive circuitfrom the other of said diodeanodes to said cathode through said networkand through a second diode-resistor, the means for unilaterallyenergizing said network with steady anode-cathode currents, including achoke-coil means conductively connected between a diodeanode connectedterminal. of one of said diodediode-resistor from said steadyanode-cathode currents, and a conductive connection between the negativeterminal of said source and said terminal of said diode resistor.

'16. A frequency discriminator having a thermionic tube with a cathode,an anode, and grid control means between said cathode and anode forcontrolling anode-cathode currents, a phasecontrolling network connectedbetween said cathode and anode for controlling phase of voltages uponsaid network in response to changes of frequency impressed upon saidgrid control means, having an inductance coil means connected in serieswith a parallel resonator-circuit having one branch including aresonator-inductance coil, said network having secondary coil meansinductively coupled with said resonatorinductance coil for transferringvoltages therefrom, a voltage-rectifying means includuing a diode meansserially connected with a dioderesistor means, a secondvoltage-rectifying means including a second diode means seriallyconnected with a second diode-resistor means, and circuit connectionsbetween said voltage-rectifying means and said phase-controllingnetwork, including a circuit through said secondary coil means.

17. A frequency demodulator having a thermionic tube with a cathode, ananode, a grid control means for controlling anode-cathode oury rents, afirst diode-anode with said cathode and a second diode-anode with saidcathode, a voltagecombining network for combining frequency responsivevoltages, including a three-branch conductive impedance circuit having acommon junction between a terminal of each of said conductive impedancebranches, one of said branches including inductance-coil means connectedfrom one of said diode-anodes to said junction, another of said branchesincluding a second inductancecoil means connected from the other of saiddiode-anodes to said junction, and a third branch having a conductiveimpedance connected from said cathode to said junction,energizing-circuit means for energizing said network with carrierfrequencies, said energizing-circuit means having mutual impedance withsaid network and including a source of unidirectional supply-voltagewith positive terminal connected to said anode; a first diode-resistorfor rectified voltage connected in one of said diode-anode connectedbranches, a second diode-resistor for rectified voltage connected in theother of said diode-anode connected branches, and conductiveoutput-circuit connections for conductively transferring frequencydemodulated voltages from said diode-resistors and opposing transfer ofcarrier frequency voltages from said network, including a circuitthrough inductance means coupled with said network.

18. The combination with a diode voltagerectifier having a cathodemeans, a diode-anode means with said cathode means, and the conductivecircuit connections between said means serially including adiode-resistor for rectified voltages shunted by a condenser forsmoothing said rectified voltages, and a conductive impedance means forimpressing alternating voltages upon said diode-anode means, of athermionic amplifier means including a second anode means with saidcathode means, and grid control means between said second anode meansand said cathode means, a source of unidirectional supply-voltage withpositive terminal connected to said second anode means, and means forunilaterally energizing said amplifier means with unidirectional currentfrom said source, including a junction-terminal consisting of thenegative terminal of said source and the diode-anode connected terminalof said diode-resistor, and chokecoil means connected to saidjunction-terminal of said diode-resistor, by-passing said unidirectionalcurrent of said second anode means to said cathode means around saiddiode-resistor.

19. A frequency-demodulator having a thermionic tube with a cathode, ananode grid control means for controlling currents between said anode andcathode, and a diode means including a diodeanode with said cathode, avoltage phase-control circuit including a, parallel resonator-circuitconnected in series with a choke-impedance means,

a circuit connection from said anode to said cathode for energizing saidphase-control circuit with carrier frequencies, serially including saidresonator-circuit, said choke-impedance means, and a diode-resistormeans for rectified voltages a. capacitor means shunted across saiddioderesistor means, and a conductive connection from said diode-anodeto said diode-resistor means for providing rectified voltages responsiveto frequen-cy upon said diode-resistor means.

, ing two inductance means mutually independent of each other, and ajunction-terminal between said inductance means; impedance meansincluding capacitance shunted across one of said inductance means forresonating said shunted inductance means with frequencies of saidcathodeanode current and with energy transferred through the other ofsaid inductance means, voltage-rectifying means including diode meansserially connected with diode-impedance means having resistor means forsaid output-voltages, said voltage-rectifying means being connectedacross both of said serially connected inductance means for rectifyingcombined voltages therefrom, a common-terminal upon said resistor meansin common with a negative terminal of said source of anode-supplyvoltage, a controlimpedance means connected from said junctionterminalto a junction between said diode-impedance means and said diode means,said controlimpedance means being capabl of passing currents of eitherpolarity with equal impedance thereto, a second control-impedance meansconnected from said junction-terminal to said common-terminal, saidsecond control-impedance means being capable of passing currents ofeither polarity with equal impedance thereto, and a circult through oneof said inductance means and through said diode-impedance means fortransferring frequency-demodulated voltages from said diode-impedancemeans, having a neutralizing-impedance means coupled with said one ofsaid inductance means and with said diode-impedance means for cancellingalternating voltages of carrier frequency in said circuit.

21. A frequency discriminator for separating 15 output-voltages ofmodulation frequency from carrier frequency-modulated input-voltages,having a thermionic tube with a cathode, an anode, and grid controlmeans between said anode and cathode for controlling anode-cathodecurrents, connections for carrying currents between said anode andcathode including a source of unidirectional anode-supply voltage withpositive terminal connected to said anode, and including a path capableof serially carrying a cathodeanode alternating current with saidfrequencymodulated carrier frequency, having an endterminal thereofconnected to said cathode, said path serially including two inductancemeans mutually independent of each other, and a junction-terminalbetween said inductance means; impedance means including capacitanceshunted across one of said inductance means for resonating said shuntedinductanc means with frequencies of said alternating current and bymeans of energy supplied through the other of said inductance means,voltage-rectifying means including diode means serially connected withdiode-impedance means having resistor means for said output-voltages,said voltage-rectifying means being connected across both of saidserially connected inductance means for rectifying combined voltagestherefrom, a common-terminal upon said resistor means in common with anegative-voltage terminal of said source of anodesupply voltage, and acontrol-impedance means connected from said junction-terminal to ajunction between said diode means and said diodeimpedance means, saidcontrol-impedance means' being capable of passing currents of eitherpolarity with equal impedance thereto.

EDWARD H. LANGE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

